<html>

<head>
  <title></title>
  <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
  <style type="text/css">
        *{margin: 0;
            padding:0;}
        #main{margin: 0px auto;position: relative;}
        #main div{overflow: hidden;position: absolute;width:  200px;height: 200px;opacity: 0.5;
            -moz-border-radius: 50%;-webkit-border-radius: 50%;border-radius: 50%;}
  </style>
</head>

<body>
  <div id="main">
    <div></div>
    <div></div>
    <div></div>
    <div></div>
    <div></div>
    <div></div>
    <div></div>
    <div></div>
    <div></div>
    <div></div>
    <div></div>
</div>
</body>
<script>
  var main = document.getElementById('main');
  var circles = main.getElementsByTagName('div');
  var st = [0,1,2,3,4,5,6,7,8,9,'a','b','c','d','e','f'];
  var json = [],arr=[],color = [];
  var maxW = 0;
  var maxH = 0;
  var cwidth = circles[0].offsetWidth;
  var cheight = circles[0].offsetHeight;

  //根据浏览器窗口的大小自动调节小球的运动空间
  window.onresize=function(){
      var main = document.getElementById('main');
      maxW=window.innerWidth-circles[0].clientWidth;
      maxH=window.innerHeight-circles[0].clientHeight;
      main.style.width = window.innerWidth+'px';
      main.style.height = window.innerHeight+'px';

  }
  onresize();
  //数组对象的初始化
  for(var i=0;i<circles.length;i++){
      arr=[];
      for(var j=0;j<6;j++){
          color[j] = st[Math.floor(Math.random()*16)];
      }
      arr.x = Math.floor(Math.random()*(maxW+1));//初始x坐标
      arr.y = Math.floor(Math.random()*(maxH+1));//初始y坐标
      arr.cx = arr.x + circles[0].offsetWidth/2;//圆心x坐标
      arr.cy = arr.y + circles[0].offsetHeight/2;//圆心y坐标
      arr.movex = Math.floor(Math.random()*2);//x轴移动方向
      arr.movey = Math.floor(Math.random()*2);//y轴移动方向
      arr.bgolor = '#'+ color.join('');//随机生成一个6位字符串
      arr.speed = 2+Math.floor(Math.random()*5);
      //随机生成一个2~6之间的移动速度（如果设置的改变速度太大，容易造成小球碰撞时两个小球之间有重合，也有可能小球会出界）
      arr.timer = null;//计时器
      arr.index = i;//索引值
      json.push(arr);
      circles[i].style.left = arr.x + 'px';//小球位置初始化
      circles[i].style.top = arr.y + 'px';//小球位置初始化
      circles[i].style.backgroundColor = arr.bgolor;//小球背景颜色初始化
  }
  //碰撞函数
  function crash(a){
      var ball1x = json[a].cx;
      var ball1y = json[a].cy;
      for(var i= 0;i<json.length;i++){
          if(i!=a){
              var ball2x = json[i].cx;
              var ball2y = json[i].cy;
              //圆心距离的平方
              var len = (ball1x-ball2x)*(ball1x-ball2x)+(ball1y-ball2y)*(ball1y-ball2y);
              if(len <= cwidth*cwidth){
              //小球位置的判断，发生碰撞反应
                  if(ball1x >ball2x){
                      if(ball1y > ball2y){
                          json[a].movex=1;
                          json[a].movey=1;
                      }else if(ball1y < ball2y){
                          json[a].movex=1;
                          json[a].movey=0;
                      }else{
                          json[a].movex=1;
                      }
                  }else if(ball1x < ball2x){
                      if(ball1y > ball2y){
                          json[a].movex=0;
                          json[a].movey=0;
                      }else if(ball1y < ball2y){
                          json[a].movex=0;
                          json[a].movey=1;
                      }else{
                          json[a].movex=0;
                      }
                  }else{
                      if(ball1y > ball2y){
                          json[a].movey=1;
                      }else if(ball1y < ball2y){
                          json[a].movey=0;
                      }
                  }
              }
          }

      }
  }
  //移动函数
  function move(circle){
      circle.timer = setInterval(function () {
          if(circle.movex == 1){
              circle.x+=circle.speed;
              if(circle.x+circle.speed >= maxW){//防止小球出界
                  circle.x = maxW;
                  circle.movex=0;//小球运动方向发生改变
              }
          }else{
              circle.x-=circle.speed;
              if(circle.x-circle.speed <= 0){
                  circle.x = 0;
                  circle.movex=1;
              }
          }
          if(circle.movey == 1){
              circle.y += circle.speed;
              if(circle.y+circle.speed >= maxH){
                  circle.y = maxH;
                  circle.movey=0;
              }
          }else{
              circle.y-=circle.speed;
              if(circle.y-circle.speed <= 0){
                  circle.y = 0;
                  circle.movey=1;
              }
          }
          circle.cx = circle.x + circles[0].offsetWidth/2;//小球每一次运动圆心都会发生改变
          circle.cy = circle.y + circles[0].offsetHeight/2;
          circles[circle.index].style.left = circle.x + 'px';//小球位置重定位
          circles[circle.index].style.top = circle.y + 'px';
          /*console.log('x'+circle.cx+'y'+circle.cy);*/
          crash(circle.index);
      },15);
  }
  //对每一个小球绑定计时器，让小球动起来
  for(var i=0;i<circles.length;i++){
      move(json[i]);
  }
</script>
</html>